Applicant is aware of U.S. Pat. No. 5,603,168 which issued to McMahon, Jr. on Feb. 18, 1997 for a Method and Apparatus for Controlling a Dryer wherein it is taught that the cooling section cools into the material exiting the drying chamber of the dryer by blowing ambient air around the material as it travels through the cooling section. A control is provided for maintaining the pressure within the cooling section at a level greater than the pressure in the drying chamber. By operating the cooling section at a slightly higher pressure, leakage of exhaust gases from the drying chamber into the cooling section is inhibited. An automatic control for maintaining the required pressure differential between the cooling section and the drying chamber pressure is described. Pressure sensors are disclosed for monitoring the pressure in the drying chamber and the pressure in the cooling section. A controller was suggested to be connected to the pressure sensors and operatively coupled to a damper for controlling the flow of cooling air thereby controlling the pressure within the cooling section. Alternately, the speed of a cooling air blower may be adjusted. Applicant is also aware of U.S. Pat. No. 4,439,930 which issued Apr. 3, 1984 to McMahon, Jr. Both U.S. Pat. Nos. 5,603,168 and 4,439,930 are incorporated herein by reference.
Conventionally, the last structural units (sections), typically one to four, sections of veneer jet dryers comprise the cooling zone. They are typically fitted with vane axial-type supply air fans and motors delivering outside air to nozzle systems for direct cooling of the veneer passing through the heating and cooling sections. It is typically desirable to utilize the cooling zone to drop the surface temperature of the veneer to a specified level. This has typically been accomplished by turning certain sections of the cooling zone “on or off” as necessary to achieve the desired temperature, or to utilize an alternating current (AC) variable speed drive on the fan motors to vary the speed of the fans and, thereby, vary the veneer temperature. Being that these cooling sections are typically connected directly, that is, in fluid communication with the heated sections of the dryer, with only a baffle wall separating the two, there has not been the ability to control the flow of cooling zone air into or out of the dryer. This has resulted in either “cool” air being pushed into the heated drying process or heated process air flowing into the cooling zone specifically when the damper described in U.S. Pat. No. 5,603,168 is not present or set too far open.
The present invention contemplates an improved automatic control for maintaining the required pressure differential between the cooling section and the drying chamber. Pressure sensors are disclosed for monitoring the pressure in the drying chamber and the pressure in the cooling section. A controller connected to the pressure sensors is operatively coupled to a damper for controlling the flow of cooling air out of the dryer thereby controlling the pressure within the cooling section above dryer pressure. Alternately, the speed of a cooling air blower may be adjusted.